Sixty-six individuals representing 54 families were studied (Supplementary Material, Table S1). All individuals were found to harbor two ABCA4 variants likely to cause the retinal disease (18,20–26). In 40 families (74%), independent segregation of the two alleles was demonstrated. The ages at the time of their first visit ranged from 9 to 74 years (mean = 35.9, median = 35.2 years); in the majority of individuals (36/66=55%), data were available from a second visit that occurred on average 8.7 years (range=2–20 years, median = 6.9 years) after the first visit.

Over 200 ABCA4 sequence variants have been reported so far in patients with STGD and other retinopathies1,5,6,7,8,9,10,11,12,13,14,15,16,17. We have examined 33 missense mutations, 3 small in-frame deletions and 1 frameshift near the carboxy terminus (Table 1 and Fig. 2), including those mutations most commonly encountered in STGD patients1,5,6,7,8,9,10,11 and several that were reported in AMD patients15. As an initial step in assessing protein folding and stability, we analysed each ABCR variant by immunoblotting and azido-ATP labelling (Fig. 3). Mutations that cause small deletions (delVVAIC1681 and delPAL1761) or introduce charged amino acids into predicted transmembrane domains (G851D and G1886E) produce greatly reduced amounts of protein. Among the ABCR variants that are expressed with normal or nearly normal yield, azido-ATP labelling revealed a subset that is defective in ATP binding. A variety of mutations that lie outside of the nucleotide-binding domains (NBDs) can impair azido-ATP labelling, including L541P, predicted to reside adjacent to a transmembrane domain, and W1408R, which resides between the homologous halves of ABCR (Fig. 2). These data suggest that ATP binding to the NBDs is allosterically coupled to conformational changes in or near the transmembrane regions. Moreover, some mutations within either of the two NBDs abolish or nearly abolish all azido-ATP labelling, as seen, for example, with variants T971N, L1971R, G1977S and E2096K, implying allosteric coupling between the two NBDs, as described for P-glycoprotein22,23.Table 1 Naturally occurring ABCR variants produced in transfected 293 cellsFull size tableFigure 2: Locations of 37 naturally occurring ABCR sequence variants and 4 synthetic mutations.The predicted transmembrane topography and domain structure of ABCR is based on the hydropathy profile and sequence alignment with other ABC transporters. The cytosolic face of the membrane is downward. NBD, nucleotide binding domain; HH, highly hydrophobic domain shared with other members of the ABC1/ABCR subfamily of ABC transporters. A, B and C indicate the sequence motifs characteristic of nucleotide binding folds. Asterisks denote the four synthetic mutations.Full size imageFigure 3: Protein yield and ATP-binding capacity of 37 naturally occurring ABCR variants produced in transiently transfected 293 cells.Membranes were analysed by immunoblotting with affinity-purified anti-ABCR antibodies (top) and photoaffinity labelling with α-32P azido-ATP (bottom). We loaded 1 μg (immunoblotting) or 2.5 μg (azido-ATP labelling) of total membrane protein, as determined by Bradford assay, per track. The mutations that reside in NBD-1 and NBD-2 are indicated above the corresponding lanes. The relative levels of the different variant proteins and the extent of azido-ATP labelling were observed to be highly reproducible in multiple independent experiments. ABCR (large arrowhead); an endogenous 55-kD protein (small arrowhead) serves as an internal control for azido-ATP labelling. Molecular mass standards are shown on the left in kD.Full size imageThe combination of immunoblotting and azido-ATP labelling revealed defects in more than 75% of the variants tested. Among the variants with reduced yield and/or ATP binding are G863A and delG863, the two protein products of a guanosine2588→cytosine mutation that both generates a glycine-to-alanine substitution at codon 863 and activates a cryptic splice acceptor site in exon 17 that results in the removal of codon 863 from approximately 50% of the transcripts10. This is the most common allele among STGD patients in Northern Europe, representing roughly 20% of disease-associated alleles. It is also present at a frequency of approximately 3% in the general population in Northern Europe and approximately 1% in the United States population7,9,10. Genotype-phenotype correlations suggest that it is a mild allele and that it leads to STGD only when paired with a more severe allele10. Relative to wild type, the G863A variant is subtantially impaired and the delG863 variant is mildly impaired (Fig. 3).

Case 3A 15-year-old female presented with complaints of difficulty reading materials held greater than 6 inches from her eyes. She was clinically diagnosed with STGD 4 years prior and noted decreased visual acuity since age seven, which stabilized over the past few years. Family history was not significant for ocular disease. Best-corrected visual acuity was 20/150 OU. Anterior segment exam was unremarkable with applanation tonometry measuring 16 mmHg OU. Posterior segment exam and autofluorescence was significant for bilateral central atrophy and pisciform fleck atrophy involving the peripapillary, macular, and peripheral regions OU (Figure 3, A and B). Genotyping was significant for ABCA4 mutations P1380L and R2030Q.Open in a separate windowFig. 3A and B, Case 3. STGD mutations P1380L and R2030Q. Autofluorescence OD and OS demonstrate atrophic fleck lesions involving the macula and periphery with an area of confluent atrophy superotemporal to the fovea OD. Hyperautofluorescent flecks are also present in the periphery OU. The peripapillary regions reveal atrophic flecks OU without areas of confluent atrophy.

Case 2A 19-year-old female referred for consultation for difficulty reading, particularly in dim light. She was clinically diagnosed with STGD 3 month prior, after complaining of gradual difficulty in focusing. Family history was not significant for ocular disease. Visual acuity measured 20/40 OD and 20/150 OS. Slit-lamp examination was unremarkable with normal anterior segments and applanation tensions of 14 mmHg OU. Funduscopic exam revealed bilateral central atrophy, multiple fleck lesions, multiple clumps of yellowish deposits at the level of the retinal pigment epithelium in the posterior pole surrounded with some pigment clumping, and no evidence of atrophy of the retinal pigment epithelium. Autofluorescence imaging revealed multifocal atrophic lesions involving the central macula and peripheral hyperautofluorescent flecks OU. The peripapillary regions demonstrated atrophic flecks OU without confluent atrophy (Figure 2, A and B). Genotyping revealed homozygous ABCA4 mutations, P1380L and P1380L.Open in a separate windowFig. 2Case 2. STGD mutations P1380L and P1380L. A, Autofluorescence OD. B, Autofluorescence OS show multifocal hypoautofluorescent (atrophic) lesions involving the central macula OU and peripheral hyperautofluorescent flecks OU. The peripapillary regions have atrophic flecks OU but there is not confluent peripapillary atrophy.

Case 4A 52-year-old male was examined for declining vision OS over the past few months. He was previously clinically diagnosed with STGD 7 years before presentation. Family history was not significant for ocular disease. Best-corrected visual acuity measured 20/100 OD and 20/70 OS. Spherical refractive error measured −3.00 OD and −3.25 OS. Anterior segment examination was unremarkable and applanation tonometry measured 17 mmHg OD and 14 mmHg OS. Posterior segment examination was significant for central atrophy and classic peripheral pisciform flecks sparing the peripapillary regions OU (Figure 4, A and B). Autofluorescence imaging demonstrated inner atrophic flecks and outer hyperautofluorescent flecks. Moderate peripapillary hypoautofluorescence, but not atrophy, was present, likely secondary to the patient’s myopia (Figure 4, C and D). Genotyping revealed two heterozygous ABCA4 mutations, P1380L and S1696N.Open in a separate windowFig. 4Case 4. STGD mutation IVS40 + 5G>A. A, Color Photo OU. B, Red-Free Photo OU reveal central atrophy and classic peripheral pisciform flecks sparing the peripapillary regions OU. C, Autofluorescence OD. D, Autofluorescence OS show that the innermost flecks are hypoautofluorescent, consistent with atrophy, whereas the outermost flecks are hyperautofluorescent, demonstrating excess lipofuscin. There is moderate peripapillary hypoautofluorescence that is not as dark as this patient’s central atrophy or the peripapillary atrophy of Case 1. This finding may thus be due to the patient’s myopia.

Case 1A 55-year-old male was examined for long-standing central visual impairment since age 18. Family history was not significant for ocular disease. His best-corrected visual acuity of 20/350 OD and 20/200 OS was consistent with measurements over the last 20 years. Spherical refractive error measured −3.5 OD and −2.0 OS. Anterior segment examination was unremarkable and applanation tonometry measured 17 mmHg OD and 14 mmHg OS. Posterior segment examination and autofluorescence imaging were significant for sharply demarcated central and peripapillary zones of atrophy and the absence of fleck lesions (Figure 1, A–D). Humphrey visual fields demonstrated bilateral central scotomas with eccentric fixation at the inferior border. ERG examination was subnormal and similar to results obtained 22 years ago.Open in a separate windowFig. 1Case 1. STGD with peripapillary atrophy and mutations P1380L and IVS40 + 5G>A. A, Autofluorescence OD. B, Color Photo OD. C, Autofluorescence OS. D, Color Photo OS. All show marked peripapillary and macular atrophy with a sharply demarcated zone of sparing between them. These characteristics caused initial diagnostic confusion with choroidal sclerosis.Genetic testing was employed for further diagnostic information and two heterozygous ABCA4 mutations, P1380L and IVS40 + 5G>A, were identified and classified as disease-causing alleles, thereby confirming the diagnosis of STGD.

534-05STGD2461 T→AW821RMissense4139 C→TP1380LMissense5682 G→CNoneSilent5814 A→GNoneSilent

ABCA4

A 25-year-old White man presented with bilateral central vision loss due to foveal lesions consisting of vitelliform fluid.

Case 4A 52-year-old male was examined for declining vision OS over the past few months. He was previously clinically diagnosed with STGD 7 years before presentation. Family history was not significant for ocular disease. Best-corrected visual acuity measured 20/100 OD and 20/70 OS. Spherical refractive error measured −3.00 OD and −3.25 OS. Anterior segment examination was unremarkable and applanation tonometry measured 17 mmHg OD and 14 mmHg OS. Posterior segment examination was significant for central atrophy and classic peripheral pisciform flecks sparing the peripapillary regions OU (Figure 4, A and B). Autofluorescence imaging demonstrated inner atrophic flecks and outer hyperautofluorescent flecks. Moderate peripapillary hypoautofluorescence, but not atrophy, was present, likely secondary to the patient’s myopia (Figure 4, C and D). Genotyping revealed two heterozygous ABCA4 mutations, P1380L and S1696N.Open in a separate windowFig. 4Case 4. STGD mutation IVS40 + 5G>A. A, Color Photo OU. B, Red-Free Photo OU reveal central atrophy and classic peripheral pisciform flecks sparing the peripapillary regions OU. C, Autofluorescence OD. D, Autofluorescence OS show that the innermost flecks are hypoautofluorescent, consistent with atrophy, whereas the outermost flecks are hyperautofluorescent, demonstrating excess lipofuscin. There is moderate peripapillary hypoautofluorescence that is not as dark as this patient’s central atrophy or the peripapillary atrophy of Case 1. This finding may thus be due to the patient’s myopia.

Case 1A 55-year-old male was examined for long-standing central visual impairment since age 18. Family history was not significant for ocular disease. His best-corrected visual acuity of 20/350 OD and 20/200 OS was consistent with measurements over the last 20 years. Spherical refractive error measured −3.5 OD and −2.0 OS. Anterior segment examination was unremarkable and applanation tonometry measured 17 mmHg OD and 14 mmHg OS. Posterior segment examination and autofluorescence imaging were significant for sharply demarcated central and peripapillary zones of atrophy and the absence of fleck lesions (Figure 1, A–D). Humphrey visual fields demonstrated bilateral central scotomas with eccentric fixation at the inferior border. ERG examination was subnormal and similar to results obtained 22 years ago.Open in a separate windowFig. 1Case 1. STGD with peripapillary atrophy and mutations P1380L and IVS40 + 5G>A. A, Autofluorescence OD. B, Color Photo OD. C, Autofluorescence OS. D, Color Photo OS. All show marked peripapillary and macular atrophy with a sharply demarcated zone of sparing between them. These characteristics caused initial diagnostic confusion with choroidal sclerosis.Genetic testing was employed for further diagnostic information and two heterozygous ABCA4 mutations, P1380L and IVS40 + 5G>A, were identified and classified as disease-causing alleles, thereby confirming the diagnosis of STGD.

A10M c.4139C>T:p(P1380L